Two axes of rotation of the carpometacarpal (CMC) joint of seven cadaver thumbs were located using an axis finder. The flexion-extension axis is located in the trapezium and the abduction-adduction axis is in the first metacarpal. These axes are fixed, are not perpendicular to each other or to the bones, and do not intersect. Motion of the first metacarpal on the trapezium can be defined by these two axes. Understanding of the movements of the basal joint of the thumb is essential to the study of its function and reconstruction.
A three-dimensional scalable biomechanical model of the four fingers of the hand to evaluate power grip is proposed. The model has been validated by means of reproducing an experiment in which the subjects exerted the maximal voluntary grasping force over cylinders of different diameters. The model is used to simulate the cylinder grip for two hand sizes and for five different handle diameters. The reduction of the muscle forces using different handle diameters has been studied. The model can be applied to the design and evaluation of handles for power grip and to the study of power grasp for normal and abnormal hands.
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